Departamento de Química Física, Facultade de Química, Universidade de Vigo, 36310 Vigo, Spain.
J Phys Chem A. 2011 Aug 25;115(33):9128-38. doi: 10.1021/jp2062095. Epub 2011 Jul 28.
The photochemistry of a model merocyanine-spiropyran system was analyzed theoretically at the MS-CASPT2//SA-CASSCF(14,12) level. Several excited singlet states were studied in both the closed spiropyran and open merocyanine forms, and the paths to the different S(1)/S(0) conical intersections found were analyzed. After absorption of UV light from the spiropyran form, there are two possible ultrafast routes to efficient conversion to the ground state; one involves the rupture of the C(spiro)-O bond leading to the open form and the other involves the lengthening of the C(spiro)-N bond with no photoreaction. From the merocyanine side the excited state can reach a very broad S(1)/S(0) conical intersection region that leads the system to the closed form after rotation of the central methine bond. Alternatively, rotation of the other methine bonds connects the system through different S(1)/S(0) conical intersections to several merocyanine isomers. The present work provides a theoretical framework for the recent experimental results (Buback , J. J. Am. Chem. Soc. 2010, 132, 1610-1619) and sheds light on the complex photochemistry of these kinds of compounds.
采用 MS-CASPT2//SA-CASSCF(14,12) 方法对模型美西螈螺吡喃-花青素体系的光化学进行了理论分析。在闭合的螺吡喃和开环的美西螈形式下研究了几种激发单线态，分析了找到的不同 S(1)/S(0) 交叉锥的途径。从螺吡喃形式吸收紫外光后，有两种可能的超快途径可以有效地转化为基态；一种涉及 C(spiro)-O 键的断裂，导致开环形式，另一种涉及 C(spiro)-N 键的延长，没有光反应。从花青素侧，激发态可以到达一个非常宽的 S(1)/S(0) 交叉锥区域，该区域在中央甲撑键旋转后将系统导向闭合形式。或者，另一个甲撑键的旋转通过不同的 S(1)/S(0) 交叉锥将系统连接到几个花青素异构体。本工作为最近的实验结果（Buback, J. J. Am. Chem. Soc. 2010, 132, 1610-1619）提供了理论框架，并阐明了这类化合物复杂的光化学。
